This invention relates to a fuel injection control system for a fuel-injected internal combustion engine. More particularly, it relates to a fuel injection control system that combines the advantages of digital computer calculation of a fuel injection pulse width the advantages of analog computer computation of fuel injection pulse width under conditions of engine cranking and digital computer default.
Microprocessor (digital computer) control systems for internal combustion engines recently have come into use in motor vehicale applications. Microprocessor engine control systems are described in commonly assigned U.S. Pat. Nos. 3,969,614 to Moyer et al and 4,086,884 to Moon et al. The microprocessor engine control systems described in these patents use a microprocessor, among other things, to determine a fuel injection pulse width in accordance with the requirements of engine operation. The fuel injection pulse widths are determined on a real-time basis based upon the mass rate of air induction into the engine. In this system, the fuel is injected intermittently, rather than continuously, and the time at which each injection is initiated or terminated also may be determined by the microprocessor.
A prior art problem with microprocessor control of engine operatin is the disablement of the engine and associated motor vehicle in the event the computer enters a default mode. In such case, with the prior art system, there would not be a proper digital computer determination of the quantity of fuel to be metered to the engine and engine operation could cease.
A second problem associated with the prior art digital computer engine control systems is the inability of the digital computer to function accurately during engine cranking. The digital computer systems utilize a number of inputs which are indicative of engine operation. These may include intake manifold pressure, engine crankshaft position and speed, engine operating temperature, and some less important parameters that may include barometric temperature and pressure and perhaps EGR valve position as well. During engine cranking, the data inputs to the digital computer are very limited and precise determination of required fuel quantity is difficult to determine.